Circuitry for matching the up and down impedances of a voltage-mode transmitter

Some embodiments of the present invention provide a voltage-mode transmitter. The transmitter can include configuration circuitry, bias circuitry, and a set of driver slices. Each driver slice can include driver transistors which drive an output value. The outputs of each driver slice can be directly or capacitively coupled with the transmitter's outputs. Each driver slice can also include one or more impedance-matching transistors which are serially coupled to at least some of the driver transistors. The configuration circuitry can configure a subset of driver slices so that the down (or up) impedance of the transmitter is within a first tolerance of a desired impedance value. The bias circuitry can bias the one or more impedance-matching transistors in each driver slice in the subset of driver slices so that the up (or down) impedance is within a second tolerance of the down (or up) impedance.